In a sentencing indication ruling, Judge Bruce Davidson said it was worrying the defendant was carrying a knife in a public place.
"Any offending involving the use of a knife carries an ever-present risk of really serious injury, if not death," he said.
"The victim was also vulnerable at the time in the sense that he was directly engaged in scuffle with someone else."
Judge Davidson said a "sense of reality needs to be brought to bear in the cold hard light of day in a courtroom".
"This could easily be categorised as a significant overreaction, but this was an altercation involving a large group of people on New Year's Eve, many undoubtedly fuelled by alcohol.
"Apart from the use of the knife, the troubling feature is the defendant was carrying it, and when the circumstances arose, was prepared to use it. However, in my view, there are is a sense that the circumstances as they unfolded before her, led to her impulsive and spontaneous reaction."
In the Wellington District Court today, Judge Davidson said Ruru Mahara had carried out some voluntary counselling and community work.
"You have excellent employment where you are highly regarded and where you have genuine future managerial prospects," he said.
"Protection of your employment must be an imperative sentencing consideration."
He also said she had done "very well" since returning to New Zealand, and sentencing should reflect that.
Judge Davidson sentenced her to six months of community detention with six months' post-release conditions.
